Water Intake Calculator: How Much Water Should You Drink a Day?
Answer 7 quick questions about your body, activity and climate to get your personal daily water target, how to spread it through the day, and how much more to drink on workout days.
Step 1
Men's and women's water needs differ, partly because of body size.
Step 2
Thirst gets weaker with age, so older adults can get dehydrated without feeling thirsty.
Please enter an age between 18 and 100. Children's needs are different, so ask a pediatrician.
Step 3
A bigger body holds and uses more water.
Please enter a weight between 80 and 500 lb (36–227 kg).
Step 4
Sweat is the biggest thing that changes your water needs from one day to the next.
Step 5
Heat and humidity make you sweat even when you're sitting still.
Step 6
About a fifth of your water comes from food. Watery foods count.
Last step
Some conditions change how much water is safe, so your answer matters.
Estimating your daily water loss…
“Drink 8 glasses a day” is easy to remember, but it’s wrong for most people. A 120 lb office worker and a 220 lb roofer in July need very different amounts. This calculator asks the 7 things that actually change your water needs and gives you a daily target in ounces or liters, plus how to spread it through your day.
How this water intake calculator works
- Body weight and sex set your baseline. We start at about 35 mL of total water per kg of body weight. We then keep that within the official adequate intakes: 2.0–2.7 liters a day of total water for women and 2.5–3.7 liters for men (the European and US reference values).
- Food counts. About 20% of the water you take in comes from food, more if you eat a lot of fruit, vegetables and soup. The calculator subtracts it, so your result is what you need to drink.
- Exercise adds back what you sweat. People lose 0.5 to 2 liters of sweat per hour of exercise, depending on intensity, body size and heat. The calculator shows a separate, higher number for exercise days.
- Heat and humidity add 8–34 oz (0.25–1 liter) a day, and they make exercise sweat about 25% heavier.
- Age matters because thirst gets weaker after about 65. For older adults we never go below the geriatric guideline of 1.6 liters (women) or 2.0 liters (men) of drinks a day.
- Pregnancy and breastfeeding add about 300 mL and 700 mL a day. Heart failure and kidney disease often require a fluid limit, so the calculator won’t give a number for those.
How much water should you drink a day? Typical results
Here’s what the calculator gives for healthy adults with a typical diet, in a mild climate and without exercise. Add more for exercise and heat.
| Body weight | Women (drinks per day) | Men (drinks per day) |
|---|---|---|
| 120 lb (54 kg) | 55 oz (1.6 L) | 70 oz (2.0 L) |
| 150 lb (68 kg) | 65 oz (1.9 L) | 70 oz (2.0 L) |
| 180 lb (82 kg) | 75 oz (2.2 L) | 80 oz (2.3 L) |
| 220 lb (100 kg) | 75 oz (2.2 L) | 95 oz (2.8 L) |
For comparison, “8 glasses a day” is 64 oz (1.9 L). That’s close for an average adult in a cool climate, but too little for bigger, active people or anyone working in the heat. We take the 8-glasses rule and other hydration myths apart in how much water should you actually drink.
How much extra water to drink when you exercise
The American College of Sports Medicine’s advice is to drink enough to avoid losing more than about 2% of your body weight in sweat during exercise. For most people that means:
- Before: about 5–7 mL per kg (roughly 12–16 oz for most adults) in the 4 hours before you start.
- During: sip regularly in sessions longer than about an hour, guided by thirst.
- After: weigh yourself before and after a hard session. Replace each pound you lost with about 20–24 oz of fluid over the next few hours.
For long or very sweaty sessions, plain water isn’t enough on its own, because you also lose sodium. See electrolytes: why water alone isn’t always enough.
Signs you’re drinking enough (or too little)
- Pee color is the simplest check. Pale yellow, like lemonade, is good. Dark yellow or apple juice means drink more. Clear all day may mean you’re overdoing it.
- Know the warning signs: see our full guide to dehydration symptoms, including the signs that need medical help.
- Thirst is a reliable guide for most healthy adults under 65. Older adults should drink on a schedule, because thirst weakens with age.
- Common signs of mild dehydration: headaches, tiredness, poor focus, dizziness when standing, and dark, infrequent urination.
Does coffee count toward your water intake?
Yes. In a controlled study, men who drank 4 cups of coffee a day were just as well hydrated as when they drank the same amount of water. Tea, milk, sparkling water and other drinks count too. Alcohol is the exception: it does increase fluid loss, and it also disrupts your sleep (see alcohol and sleep).
Can you drink too much water?
Yes, though it’s rare outside of long endurance events and drinking challenges. Drinking far more than you sweat can dilute the sodium in your blood (hyponatremia), which can be dangerous. Healthy kidneys can only clear about 0.8–1 liter an hour, so don’t drink more than about 1 liter (34 oz) an hour, and during marathons and similar events, drink to thirst rather than on a fixed schedule.
Who should not use this calculator
- People with heart failure, kidney disease or liver disease, or anyone told to limit fluids.
- People taking diuretics (“water pills”) or other medications that affect fluid balance.
- Children and teens.
- Anyone who is ill with fever, vomiting or diarrhea, whose needs change quickly.
This calculator is for education only and isn’t medical advice. Read our medical disclaimer. Want more tools like this? See all our free health calculators, including the protein calculator.
Sources
- EFSA Panel on Dietetic Products, Nutrition, and Allergies. Scientific Opinion on Dietary Reference Values for water. EFSA Journal. 2010;8(3):1459. doi:10.2903/j.efsa.2010.1459
- Institute of Medicine. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. National Academies Press; 2005. nap.edu
- Sawka MN, et al. American College of Sports Medicine position stand: Exercise and fluid replacement. Med Sci Sports Exerc. 2007;39(2):377-390. PubMed 17277604
- Volkert D, et al. ESPEN guideline on clinical nutrition and hydration in geriatrics. Clin Nutr. 2019;38(1):10-47. PubMed 30005900
- Thomas DT, Erdman KA, Burke LM. American College of Sports Medicine Joint Position Statement: Nutrition and Athletic Performance. Med Sci Sports Exerc. 2016;48(3):543-568. PubMed 26891166
- Armstrong LE, et al. Urinary indices of hydration status. Int J Sport Nutr. 1994;4(3):265-279. PubMed 7987361
- Killer SC, Blannin AK, Jeukendrup AE. No evidence of dehydration with moderate daily coffee intake: a counterbalanced cross-over study in a free-living population. PLoS One. 2014;9(1):e84154. PubMed 24416202
- Hew-Butler T, et al. Statement of the 3rd International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015. Br J Sports Med. 2015;49(22):1432-1446. PubMed 26227507
This article is for informational purposes only and is not medical advice. See our Medical Disclaimer before changing your exercise, diet, or supplement routine.
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Frequently asked questions
How much water should I drink a day?
Most healthy adults need about 55u201395 oz (1.6u20132.8 liters) of drinks a day, depending mainly on body size and sex, plus more for exercise and hot weather. Food supplies another 20% or so. The calculator above gives you a personal number.
How do I calculate my water intake by weight?
A common starting point is about 35 mL of total water per kg of body weight (roughly half an ounce per pound), with about 80% of that coming from drinks. Then add 16u201334 oz for each hour of sweaty exercise, and more in hot weather.
Is 8 glasses of water a day enough?
Eight 8-oz glasses (64 oz) is about right for an average-sized adult in a cool climate who does not exercise much. Bigger, more active people, and anyone in the heat, usually need more. There is no scientific basis for 8 glasses as a universal rule.
Does coffee or tea count toward water intake?
Yes. Moderate coffee and tea hydrate about as well as water, and milk, juice and sparkling water count too. Alcohol is the exception because it increases fluid loss.
How much water should I drink when exercising?
Drink about 12u201316 oz in the few hours before exercise, sip during sessions longer than an hour, and afterwards replace each pound of weight lost with about 20u201324 oz. Long, very sweaty sessions also need electrolytes, not just water.
Can you drink too much water?
Yes. Drinking far more than you sweat can dangerously dilute your blood sodium (hyponatremia). Healthy kidneys clear only about 0.8u20131 liter an hour, so avoid drinking more than about 1 liter (34 oz) an hour.
How can I tell if I am dehydrated?
Dark yellow urine, peeing rarely, thirst, headaches, tiredness and dizziness when you stand up are common signs. Pale yellow urine through most of the day means you are drinking enough.